The present invention relates to control systems and circuitry for operation of power-lift windows employed in motor vehicles. Typically, such power-lift or motorized windows are activated by driver or passenger actuation of a manual control switch from a neutral or center position to one of two side positions for moving the window either from the closed to the opened position or from the open to the closed position. The most common arrangement of the window motor switch utilizes a spring loaded actuator member which returns the switch to the neutral or OFF position when the operator's manual pressure on the actuator, for holding the switch in a side position, is released. Upon release of the switch actuator member, current is stopped to the motor and consequently movement of the window is terminated.
It has been found desirable to provide a function mode for the window lift motor operation in which the driver need only momentarily actuate the switch to initiate continuous motor running to lower the window to its fully open position, thereby eliminating the need for the driver to keep one hand on the switch actuator for more than a brief moment. If only momentary actuation of the window motor switch is required, the driver thus has one hand free to reach for a toll card, currency or other items needed for various reasons. Thus, it has been desired to provide a functional mode at operation of vehicle power-lift windows in which the driver need only momentarily actuate the motor switch to initiate continuous motor operation for lowering the window to the fully open position; and, such a functional mode of operation is referred to as "EXPRESS" window operation.
Where the aforesaid EXPRESS window lift motor operation is desired in a vehicle, it has been found particularly troublesome and costly to provide a way or means of sensing the lower limit condition of the window movement and thereupon automatically providing for shut-OFF of current to the window lift drive motor. Heretofore, a known technique for sensing the lower limit or fully open position of the window has employed a means for sensing the increase in motor current as the motor approached stall when the window movement mechanism contacted the limit stop in the fully lowered or open position. This aforesaid technique of permitting the motor current to rise significantly in order that motor stall can be detected, has resulted in prohibitively high loads on the window lift actuating mechanism and decreased window lift motor life. It has thus been desired to find a way of lower limit position operation of a vehicle window in a manner which prevented a substantial increase in motor current upon the motor stalling as the window came to rest against the lower limit stop.